Behavioral Selectivity: Species-Specific Effects of Nutmeg, Cinnamon, and Clove Essential Oils on Sitophilus oryzae and Its Parasitoid Lariophagus distinguendus

Abstract

The integration of essential oils (EOs) with biological control agents offers a promising alternative to synthetic pesticides, though compatibility remains unclear. This study evaluated nutmeg (Myristica fragrans, NM), cinnamon (Cinnamomum verum, CIN), and clove (Syzygium aromaticum, CL) specifically on S. oryzae and L. distinguendus. Olfactory and behavioral responses to whole EOs and major constituents (myristicin, cinnamaldehyde, eugenol) were analyzed using the area preference method (APM) and two-choice behavioral bioassay (TCB), with confirmation by gas chromatography-mass spectrometry (GC-MS). In S. oryzae, APM showed attraction to all three EOs (PI = 0.14 to 0.56). A paradox emerged, however, as single constituents were mostly repellent (eugenol: PI = -0.58 to -0.70; cinnamaldehyde: PI shifted from 0.16 to -0.20), underscoring the complexity of EO mixtures where multiple compounds act jointly rather than individually. In contrast, L. distinguendus strongly avoided CL and CIN in TCB, with fewer than 30% of parasitoids choosing the EO-treated side (χ² test, p < 0.05). CIN therefore demonstrated selective potential, simultaneously attracting S. oryzae while repelling L. distinguendus. These findings highlight the dual role of EOs as botanical pest control tools, while stressing the need to consider non-target effects before practical application.

Keywords: attractiveness; behavioral responses; multi-trophic interactions; repellency; rice weevil; stored-product pest.

Figure 1

Behavioral responses assessed in a two-choice olfactometer bioassay of (above) Sitophilus oryzae and (below) Lariophagus distinguendus to clove (CL), cinnamon (CIN), and nutmeg (NM) essential oils, tested at three concentrations: 0.1% (CL0.1, CIN0.1, NM0.1 = 0.24 µL L⁻¹ air equivalent), 1% (CL1, CIN1, NM1 = 2.39 µL L⁻¹ air equivalent), and 5% (CL5, CIN5, NM5 = 11.95 µL L⁻¹ air equivalent). Asterisks indicate a significant difference from a 50:50 distribution between control and treatment (*, p < 0.05; χ² test). Values are means ± SD (n = 30 per treatment).

Figure 2

Diagram of the Two-Choice Behavioral Bioassay (TCB) used to test the olfactory responses of Sitophilus oryzae and its parasitoid Lariophagus distinguendus to EOs. Individual insects were released into a central chamber and allowed to choose between a control and EO stimulus, each presented on a square piece of filter paper in opposing chambers.

Figure 3

Schematic representation of the Area Preference Method (APM) used to evaluate the behavioral responses of Sitophilus oryzae to EOs and main compounds. A treated and an untreated semicircle of filter paper were placed inside a Petri dish, allowing insects to move freely. Insect position was recorded after 24 h to calculate the Preference Index (PI).